全文获取类型
收费全文 | 404255篇 |
免费 | 4701篇 |
国内免费 | 1365篇 |
专业分类
电工技术 | 7599篇 |
综合类 | 317篇 |
化学工业 | 59935篇 |
金属工艺 | 16430篇 |
机械仪表 | 13496篇 |
建筑科学 | 8352篇 |
矿业工程 | 2154篇 |
能源动力 | 11536篇 |
轻工业 | 28508篇 |
水利工程 | 4267篇 |
石油天然气 | 7913篇 |
武器工业 | 17篇 |
无线电 | 49292篇 |
一般工业技术 | 83042篇 |
冶金工业 | 75118篇 |
原子能技术 | 9190篇 |
自动化技术 | 33155篇 |
出版年
2022年 | 2555篇 |
2021年 | 3894篇 |
2020年 | 2940篇 |
2019年 | 3807篇 |
2018年 | 6490篇 |
2017年 | 6479篇 |
2016年 | 6923篇 |
2015年 | 4320篇 |
2014年 | 7142篇 |
2013年 | 20042篇 |
2012年 | 11424篇 |
2011年 | 15281篇 |
2010年 | 12146篇 |
2009年 | 13731篇 |
2008年 | 14070篇 |
2007年 | 13827篇 |
2006年 | 12432篇 |
2005年 | 11126篇 |
2004年 | 10520篇 |
2003年 | 10431篇 |
2002年 | 9841篇 |
2001年 | 9744篇 |
2000年 | 9155篇 |
1999年 | 9539篇 |
1998年 | 24392篇 |
1997年 | 16735篇 |
1996年 | 12828篇 |
1995年 | 9545篇 |
1994年 | 8380篇 |
1993年 | 8393篇 |
1992年 | 6065篇 |
1991年 | 5699篇 |
1990年 | 5681篇 |
1989年 | 5326篇 |
1988年 | 5046篇 |
1987年 | 4428篇 |
1986年 | 4307篇 |
1985年 | 4815篇 |
1984年 | 4424篇 |
1983年 | 3998篇 |
1982年 | 3655篇 |
1981年 | 3733篇 |
1980年 | 3437篇 |
1979年 | 3329篇 |
1978年 | 3337篇 |
1977年 | 3751篇 |
1976年 | 4857篇 |
1975年 | 2852篇 |
1974年 | 2663篇 |
1973年 | 2730篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
A Matsumori Y Matoba R Nishio T Shioi K Ono S Sasayama 《Canadian Metallurgical Quarterly》1996,222(3):678-682
We investigated hepatitis C virus (HCV) infection in 35 patients with hypertrophic cardiomyopathy and 40 patients with ischemic heart disease who were consecutively admitted to our hospital. Frequency of positive anti-HCV antibody was significantly higher in patients with hypertrophic cardiomyopathy (6 of 35 patients, 17.1%) than that in patients with ischemic heart disease (1 of 40 patients, 2.5%, p = 0.036). In three of these six patients with hypertrophic cardiomyopathy, HCV RNA was detected in myocardial tissue. In two of these three patients, HCV RNA was detected from biopsy and autopsy specimens of the ventricles, but not in the serum, suggesting that HCV may replicate in myocardial tissue and may be relevant to ventricular hypertrophy. Thus, HCV infection may play a role in the development of hypertrophic cardiomyopathy. 相似文献
952.
JF Delaloye S Leyvraz E Outcha Adjahoto J Bauer P De Grandi 《Canadian Metallurgical Quarterly》1996,19(2):204-206
We report two cases of metastatic non-functioning pancreatic endocrine tumour with very elevated plasma levels of alpha-fetoprotein. In these two cases, serial plasma levels of alpha-fetoprotein, initially normal, correlated well with hepatic tumour progression and were associated with fatal outcome. These results suggest that elevated plasma concentration of alpha-fetoprotein may be caused by metastatic pancreatic endocrine tumour and than alpha-fetoprotein serial measurement may be useful in prognostic evaluation. 相似文献
953.
Gaidis M.C. Friedrich S. Segall K. Prober D.E. Szymkowiak A.E. Moseley S.H. 《Applied Superconductivity, IEEE Transactions on》1996,6(1):1-4
We report the development of Nb-Ta-Al-Al2O3-Al superconducting tunnel junction structures for high energy resolution and high efficiency X-ray detection. These devices utilize a Ta X-ray absorber with superconductor “bandgap engineered” quasiparticle trapping to improve charge collection. Experimental results at 0.3 K are presented, showing energy resolution of 102 eV full-width-half-maximum for 6 keV X-rays. Collected charge is in excess of 5×106 electrons. The absorption efficiency is better than 35%. Devices thermally cycle with no change in characteristics 相似文献
954.
Russell B. Pillers Banmali S. Rawat 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(11):1809-1820
The nonlinearity of a frequency-ramped single-mode laser source to be used in optical heterodyne interferometry has been investigated. The analysis is based on mode-hopping due to variation in injection current, temperature and mismatch reflections. 相似文献
955.
Second-law-based thermodynamic analysis of two-stage and mechanical-subcooling refrigeration cycles 总被引:1,自引:0,他引:1
Thermodynamic analysis of HFC-134a vapor-compression refrigeration cycles is investigated by both the first and second laws of thermodynamics. Second-law analysis is carried out for both two-stage and mechanical-subcooling refrigeration cycles. The analysis is performed on each of the system components to determine their individual contribution to the overall system irreversible losses. It is found that most of the losses are due to a low compressor efficiency. Irreversibilities of expansion valves and condenser are also significant. In addition, it is shown that the optimum inter-stage pressure for two-stage and mechanical-subcooling refrigeration systems is very close to the saturation pressure corresponding to the arithmetic mean of the refrigerant condensation and evaporation temperatures. These results are compared with the existing practice in the industry. Furthermore, theoretical results of a two-stage refrigeration system performance are also compared with experimental values for a CFC-22 system. 相似文献
956.
Wu Ting M. Badaye T. Morishita N. Koshizuka S. Tanaka 《Journal of Superconductivity》1996,9(6):637-645
Recently, superconducting Nd1Ba2Cu3Oy (Ndl23) thin films with high superconducting transition temperature (T
c) have been successfully fabricated at our institute employing the standard laser ablation method. In this paper, we report the results of surface characterization of the Nd123 thin films using an ultrahigh vacuum scanning tunneling microscope/spectroscopy (UHV-STM/STS) and an atomic force microscope (AFM) system operated in air. Clear spiral pattern is observed on the surfaces of Nd123 thin films by STM and AFM, suggesting that films are formed by two-dimensional island growth mode. Contour plots of the spirals show that the step heights of the spirals are not always the integer or half-integer number of thec-axis parameter of the structure. This implies that the surface natural termination layer of the films may not be unique. This result is supported byI-V STS measurements. The surface morphology of the Nd123 thin films is compared with that of thec-axis-oriented Y1Ba2Cu3Sy thin films. Surface atomic images of the as-prepared Nd123 thin films are obtained employing both STM and AFM. STS measurements show that most of the surfaces are semiconductive. The results of STS measurements together with the fact that we are able to see the surface atomic images using scanning probe microscopes suggest that exposure to air does not cause serious degradation to the as-prepared surfaces of Nd123 thin films. 相似文献
957.
958.
959.
S.H. Tantawi I.Z.Selim 《材料科学技术学报》1996,12(2):95-99
The use of a natural white juice, taken from magrabe banana stem, as concrete admixture to improve mechanical and physicrvchemical properties of concrete has been studied. The compressive strength, bulk density the free lime liberated during hydration and the combined water content were determined. The results indicate that the admixture acts as a retarder in most cases and as accelerator in some ones. Also, the admixture effect on the corrosion resistance of the reinforcing steel against surrounding aggressive media has been investigated using galvanostatic polarization technique. The addition of 0.2% admixture leads to the more inhibition of the steel 相似文献
960.
Abstract: This paper describes a system of shallow and deep knowledge acquisition and representation for diagnostic expert systems. The acquisition system is integrated into a diagnostic expert system shell. Shallow knowledge is represented in a failure model as a set of cause-effect relations among the possible faults, while deep knowledge is represented in three deep models: a functional, a deep causal and a taxonomic model. The acquisition and the representation of all the models are fully integrated. The deep knowledge is used by the final expert system in order to provide the user with deep explanations of the cause-effect relations of the failure model. 相似文献